High performance catalyst systems for the synthesis of alkylenecarbonates

ABSTRACT

A catalyst of the formula (1) for the synthesis of alkylene carbonate by reacting alkylene oxide and carbon dioxide  
     L m MX n   (1)  
     wherein L is selected from a group of pyridines;  
     M is a metal atom selected from Zn, Fe, Mn, Pb and In;  
     X is a halogen atom selected from Cl, Br and I;  
     m is 1 or 2, and  
     n is 2 or 3

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to catalysts for the synthesis ofalkylene carbonates by reacting alkylene oxide and carbon dioxide.

[0003] 2. Description of the Background Art

[0004] Alkylene carbonates are used in polycarbonate synthesis, as asolvent for polymer electrolyte, an intermediate in pharmaceuticalprocess, an oxyalkylation agent in dyestuff synthesis, a protectant inprocessing plant and a solvent in textile production process.

[0005] Alkylene carbonate has been prepared by reacting carbon dioxideand alkylene oxide in the presence of a catalyst, represented in Scheme1.

[0006] wherein, R¹ and R² are each independently H, C₁-C₄ alkyl orphenyl group.

[0007] In the above reaction, however, there is a limitation thatalkylene oxide either decomposes or polymerizes at higher reactiontemperatures.

[0008] Many catalysts have been developed including inorganic salts,phosphonium halide and ammonium halides. For instance, JapaneseLaid-Open Patent No S59-13776 introduced a method of using tetraalkylhalide such as tributyl methyl phosphonium iodide as a catalyst.Japanese Laid-Open Patent No H9-67365 introduced a method of using KI asa catalyst and Japanese Laid-Open Patent No. H9-235252 describes amethod of using polystyrene copolymer containing quaternary phosphoniumgroups.

[0009] These patents claim that the product yield is 50-95% when thereaction is performed at 100-170° C. for 1-5 hours. However, in order toachieve a high yield, longer reaction time and higher reactiontemperature are required. Also the water content in the raw materials,carbon dioxide and alkylene oxide has to be reduced to a few hundredppms.

[0010] Japanese Laid-Open Patent No. H9-206846 introduced a method ofusing an ion change resin substituted with the catalysts such as CsOH,RbOH and ammonium halides. In U.S. Pat. No. 4,233,221, a method of usingDOWEX and Amberlite ion exchange resin was reported with a low yield of30-80% at 80-100° C.

[0011] Besides the above-mentioned materials, a phthalocyanine complexcontaining Co, Cr, Fe, Mn, Ni, Ti, V, or Zr has been used as catalystsAlso in Japanese Laid-Open Patent No. H7-206547, a catalyst system usinga heteropolyacid whose hydrogen ion is substituted by Rubidium or Cesiumion was introduced These two cases, however, require expensive catalystswith low yield of 30-90% at relatively high reaction temperature of120-180° C.

[0012] As mentioned above, the catalysts disclosed in the above artshave one or more problems in terms of activity, reaction condition,cost, water sensitivity, etc.

OBJECTS OF THE INVENTION

[0013] Therefore the object of the present invention is to providecatalysts for the synthesis of alkylene carbonates from alkylene oxideand carbon dioxide with a high yield and selectivity in a short reactiontime under a mild reaction condition

SUMMARY OF THE INVENTION

[0014] The present invention provide a catalyst of the formula (1) forthe synthesis of alkylene carbonate by reacting alkylene oxide andcarbon dioxide

L_(m)MX_(n)   (1)

[0015] wherein L is selected from a group of pyridines;

[0016] M is a metal atom selected from Zn, Fe, Mn, Pb and In;

[0017] X is a halogen ayom selected from Cl, Br and I;

[0018] m is 1 or 2; and

[0019] n is 2 or 3.

[0020] In particular, the catalyst of the present invention is used tosynthesize alkylene carbonate of the formula (2)

[0021] wherein R¹ and R² are each independently H, C₁-C₄ alkyl orphenyl.

[0022] The present invention also provide a method for synthesizingalkylene carbonate from alkylene oxide and carbon dioxide by using thecatalyst of the formula (1)

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present inventors have found that a catalyst L_(m)MX_(n) ismore effective than the conventional catalysts in preparing alkylenecarbonate from alkylene oxide and carbon dioxide The pyridine ligand (L)in L_(m)MX_(n) is labile enough and is easily displaced by the incomingalkylene oxide to give alkylene oxide coordinated species Thecoordinated alkylene oxide is ring-opened by the attack of the displacedpyridine to give an active species

[0024] The pyridine ligand (L) includes the compounds having thestructures of the formulae (3), (4) and (5)

[0025] wherein R³, R⁴ and R⁵ are each independently H, C₁-C₄ alkyl orphenyl, each of x, y and z is independently an integer from 0 to 3; andc is an integer from 2 to 4.

[0026] In the formula (1), MX may be a compound selected from the groupconsisting of ZnX₂, FeX₂, FeX₃, MnX₂, PbX₂, and InX₃.

[0027] The amount of the catalyst for the synthesis of alkylenecarbonate is preferably 0.005-0.1 mole per mole of alkylene oxide. Incase the amount of the catalyst used is less than 0.005 mole, reactionbecomes too slow And in case the amount of the catalyst is more than 0.1mole, the reaction rate and yield do not improve any further. Thereaction pressure of the present invention could be 10-100 atm.

[0028] Since the reaction is not greatly influenced by the presence ofnitrogen hydrogen, hydrocarbons and small amounts of water in carbondioxide and alkylene oxide, it is possible to use commercially availablecarbon dioxide and alkylene oxide without further purification step.

[0029] Considering the equipment and operating cost, it is preferable tooperate a reaction at a pressure of 10-100 atm.

[0030] The reaction temperature is preferabley 60-140° C. The reactionproceeds too slow at temperatures lower than 60° C. When the reactiontemperature is too high, alkylene oxide either decomposes or undergoes aself-polymerization reaction.

[0031] Although the above reaction could be performed in the absence ofthe solvent, it is possible to use solvent to prevent excess heatproduction during the reaction. It is preferable to use alkylenecarbonate that is produced from the raw material alkylene oxide as asolvent. For instance, ethylene carbonate is a preferable solvent whenethylene carbonate is synthesized from ethylene oxide, and propylenecarbonate is preferable when propylene carbonate is synthesized frompropylene oxide

[0032] The reaction could be performed by a batch process using thereactor provided with a stirrer or by a continuous process using abubble column The invention will be further illustrated by the followingexamples, but not limited to the examples given.

EXAMPLE 1

[0033] The catalysts of the present invention were synthesized by usingthe following method.

[0034] Preparation of (C₅H₅N)₂ZnBr₂: In a 250 ml flask 100 ml oftetrahydrofurane, ZnBr₂ (2.0 g, 8.9 mmol), pyridine (1.4 g, 17.8 mmol)were added and reacted for an hour After the reaction, the precipitatewas collected by filtration and dried under a vacuum to give 3.3 g of(C₅H₅N)₂ZnBr₂

EXAMPLE 2

[0035] A 200 ml high pressure reactor was loaded with ethylene oxide(16.80 g, 380 mmol) and (C₅H₅N)₂ZnBr₂ (383 mg, 1.0 mmol) and pressurizedwith 10 atm of carbon dioxide After increasing the temperature to 100°C., carbon dioxide was introduced again to increase the pressure to 30atm. During the course of reaction, carbon dioxide was continuouslysupplied from a reservoir tank to maintain the pressure at 30 atm.

[0036] After the reaction at 100° C. for 1 hour, the reactor was cooledto room temperature. Volatiles were removed and the solid product wasseparated and weighed to be 31.5 g The yield analyzed was 93.8% bygas-liquid chromatography and mass analysis.

EXAMPLES 3-9

[0037] The process of Example 2 was repeated by the metal (M) andhalogen atoms (X) in L_(m)MX_(n). The results are shown in Table 1 TABLE1 Example Metal halide compound Product weight (g) Yield (%) 3(C₅H₅N)₂ZnCl₂ 20.4 60.7 4 (C₅H₅N)₂ZnI₂ 27.0 95.8 5 (C₅H₅N)₂FeBr₂ 26.578.9 6 (C₅H₅N)₂FeBr₃ 27.0 80.3 7 (C₅H₅N)₂PbI₂ 23.7 70.5 8 (C₅H₅N)₂MnBr₂26.7 79.5 9 (C₅H₅N)₂InCl₃ 24.6 73.1

EXAMPLES 10-17

[0038] The process of Example 2 was repeated by varying pyridine ligands(L) in L_(m)ZnBr₂ The results are shown in Table 2. TABLE 2 ExamplePyridine ligand (L) Product weight (g) Yield (%) 10 2-methyl pyridine32.2 95.8 11 2-ethyl pyridine 32.3 96.2 12 2-propyl pyridine 31.2 93.013 2-n-butyl pyridine 30.3 90.1 14 2-phenyl pyridine 30.1 89.5 151,2-bis(4-pyridyl) 31.6 94.1 ethane 16 1,2-bis(2-pyridyl) 30.5 90.7ethane 17 Polyvinylpyridine 31.3 93.1

EXAMPLES 18-21

[0039] The reactions were performed under the identical conditions as inExample 2 except the reaction temperature was varied in the range60-120° C. The results are shown in Table 3. TABLE 3 Reaction ExampleTemperature (° C.) Product weight (g) Yield (%) 18  60 12.0 35.7 19  8029.6 88.1 20 100 31.5 93.6 21 120 31.9 95.1

EXAMPLE 22-24

[0040] The reaction was performed under the identical condition as inExample 2 except that the reaction pressure was varied in the range20-100 atm. The results are shown in Table 4. TABLE 4 Example ReactionPressure (atm) Product weight (g) Yield (%) 22 20 30.9 91.9 23 50 31.593.8 24 100  32.0 95.3

EXAMPLES 25-28

[0041] The reaction were performed under the identical condition as inExample 2 except that the molar ratio of (C₅H₅N)₂ZnBr₂ to ethylene oxidewas varied in the range of 0.0005-0.1%. The amount of ethylene oxide wasfixed at 16.80 g (380 mmole) The results are shown in Table 5. TABLE 5Catalyst/ethylene oxide Example (molar ratio) Product weight (g) Yield(%) 25 0.0005 20.2 60.1 26 0.001 31.0 93.8 27 0.01 32.9 98.1 28 0.1 33.198.5

EXAMPLE 29-32

[0042] The reactions were performed under the identical condition as inExample 2 except that different alkylene oxides was employed. Theresults are shown in Table 6. TABLE 6 Example Alkylene oxide Productweight (g) Yield (%) 29 Propylene oxide 38.0 98.0 30 2-methyl-1,2-epoxy40.5 91.1 propane 31 2,3-epoxy butane 39.4 88.6 32 Styrene oxide 61.097.8

EXAMPLE 32-33

[0043] The reaction were performed under the identical condition as inExample 2 except that ethylene carbonate or propylene carbonate was usedas a solvent. The amount of the solvent used was 200 % of ethylene oxideby weight The results are shown in Table 7. TABLE 7 Example SolventProduct weight (g) Yield (%) 32 Ethylene carbonate 31.5 93.8 33Propylene carbonate 31.5 93.8

[0044] According to the present invention, alkylene carbonates can beproduced in high yield at relatively low temperature and pressure byusing the catalyst of the formula (1). The catalyst of the presentinvention has several advantages in terms of economical point of viewbecause it is inexpensive, highly active and reusable

[0045] As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the meets and bounds of theclaims, or equivalence of such meets and bounds are therefore intendedto be embraced by the appended claims.

What is claimed is:
 1. A catalyst of the formula (1) for the synthesisof alkylene carbonate by reacting alkylene oxide and carbon dioxideL_(m)MX_(n)   (1) wherein L is selected from a group of pyridines; M isa metal atom selected from Zn, Fe, Mn, Pb and In; X is a halogen atomselected from Cl, Br and l; m is 1 or 2; and n is 2 or
 3. 2. Thecatalyst of claim 1 wherein said alkylene carbonate has a structure ofthe formula (2)

wherein R¹ and R² are each independently H, C₁-C₄ alkyl or phenyl. 3.The catalyst of claim 1 wherein the pyridine ligand L has a structureselected from the group consisting of the formulae (3), (4) and (5)

wherein R³, R⁴ and R⁵ are each independently H, C₁-C₄ alkyl or phenyl,each of x, y and z is independently an integer from 0 to 3, and c is aninteger from 2 to
 4. 4. The catalyst of claim 1 wherein MX in theformula (1) is a compound selected from the group consisting of ZnX₂,FeX₂, FeX₃, MnX₂, PbX₂ and InX₃.
 5. A method for synthesizing alkylenecarbonate from alkylene oxide and carbon dioxide by using any catalystaccording to claims 1 to 3
 6. The method according to claim 5 whereinthe molar ratio of the catalyst to alkylene oxide is in the range0,0005-0.1:1.
 7. The method according to claim 5 , wherein the reactionis in the range 60-140° C.
 8. The method according to claim 5 whereinthe reaction pressure is in the range of 10-100 atm.
 9. The methodaccording to claim 5 wherein the reaction is carried out in the absenceof a solvent.
 10. The method according to claim 5 , wherein alkylenecarbonate is used as a solvent
 11. The method according to claim 10wherein the solvent is selected from ethylene carbonate and propylenecarbonate